A wireless LAN (local area network) system is one example of a general wireless communication system. FIG. 1 is a schematic diagram illustrating an exemplary wireless LAN system that is suggested in IEEE 802.11.
As shown in FIG. 1, the wireless LAN system has, as a basic unit, a basic service set (BSS) 100. BSS 100 includes at least one wireless terminal or “station” 104 and an access point (AP) 102. Two basic service sets (BSS-A, BSS-B) are depicted in FIG. 1. As shown in FIG. 1, the two basic service sets BSS-A and BSS-B may be connected with each other through a distribution system (DS) 110. BSS-A and/or BSS-B may also be connected with the Internet or with other external processing servers through a wire network or a wireless network.
The above-described wireless LAN system may communicate in a 5 GHz band using orthogonal frequency division multiplexing (OFDM) as suggested as a standard in version “a” of the IEEE 802.11 standard (i.e., IEEE 802.11a). Alternatively, the wireless LAN system may communicate in a 2.4 GHz band using direct sequence spread spectrum (DSSS) as suggested as a standard in version “b” of the IEEE 802.11 (i.e., IEEE 802.11b).
As will be understood by persons of skill in the art, orthogonal frequency division multiplexing (OFDM) refers to multi carrier digital wave modulation multiple access technique that may support hundreds of carriers. OFDM may provide for increased transmission rates per unit bandwidth and may reduce or prevent multi-route interference. Each of the carriers is designed to have an orthogonal relationship to each of the other carriers. Since the orthogonal frequency division multiplexing (OFDM) can multiplex more carriers per unit bandwidth than can be multiplexed using a general frequency division multiplexing technique, OFDM systems can provide for increased transmission rates per unit bandwidth.
Direct sequence spread spectrum (DSSS) refers to a method in which pseudo-random noise sequences that are orthogonal with one another are added to an origin signal within a predetermined frequency bandwidth for transmission and reception. The transmitter and receiver share the pseudo-random noise sequences such that data transmission and reception for a plurality of users can be made over a single channel.
Wireless LAN systems may be configured to support both the orthogonal frequency division multiplexing technique of IEEE 802.11a and the direct sequence spread spectrum technique of IEEE 802.11b. To facilitate this, a network interface card for the physical interface to the wireless LAN has been developed that supports dual mode IEEE 802.11a/b or tri-mode IEEE 802.11a/b/g.
FIG. 2 is a block diagram depicting a conventional wireless communication system for transmitting and receiving data between one of the wireless terminals and an access point in the wireless LAN system of FIG. 1. As shown in FIG. 2, the wireless communication system transmits and receives data using a single wireless channel 206 between the access point 202 and the wireless terminal 204.
FIG. 3 is a block diagram of the access point 202 and the wireless terminal 204 in the wireless communication system of FIG. 2. As described previously, the access point 202 is a device that is used to interface the wireless terminals to an external communication network such as, for example, the Internet, a satellite broadcasting network or a cable network. Thus, the access point 202 allows the user of the wireless terminal 204 to access services provided on an external network such as the Internet or games. Further, in a special case, the access point 202 can use data stored within the access point 202 to provide one or more services to users without interfacing with an external network. This is called an ad-hoc mode in the wireless LAN. In the ad hoc mode, the access point 202 not only interfaces the wireless terminal 204 to an external service network, but it also can construct a data service network in itself.
FIG. 4 is a flowchart illustrating a procedure for data transmission and reception between the access point 202 and the wireless terminal 204 of FIG. 3. In the example of FIG. 4, the data flow illustrated is the date flow associated with a user that is watching a bi-directional high definition television set (HD-TV) while sending an e-mail through the Internet by using the access point 202 and the wireless terminal 204. As shown in FIG. 4, the access point 202 transmits broadcasting data 401 from a broadcasting server (not shown in FIG. 4) to the wireless terminal 204. The wireless terminal 204 may also transmit response signals (ACK) to the broadcasting data 401 and/or broadcasting control signals (volume, channel, etc.) to the access point 202. The wireless terminal 204 also transmits mail data 412 that is generated by the user of the wireless terminal 204 to a mail server (not shown in FIG. 4) through the access point 202. A response signal to the mail data 412 may also be transmitted from the access point 202 to the wireless terminal 204.
In the example of FIG. 4, the data processor 318 resident at the wireless terminal 204 (see FIG. 3) may perform multiple different applications simultaneously such as transmission of the mail data 412 and display of the HD-TV signal 411 using the broadcasting data 401 received from the access point 202. The data processor 318 also performs protocols 413 and 414 for execution and transmission of the corresponding applications 411 and 412. The protocols performed in the wireless LAN system are exemplified as a resource reservation protocol (RSVP) for reserving/securing the band needed for the communication, and a transmission control protocol/Internet protocol (TCP/IP) for performing routing functions on the Internet.
The MAC control unit 314 on the wireless terminal 204 (see FIG. 3), through a wireless channel interface unit 312, checks the state of the wireless channel 206 for communication. If the wireless channel 206 is available, the interface unit 312 occupies the channel 206. Once the channel 206 is occupied, the wireless channel interface unit 312 transmits 417 data (e.g., mail, response signals, control signals, etc.) from the data processor 318 to the access point 202 over the wireless channel 206, and receives 418 data (broadcasting data, response signals, etc.) from the access point 202 and forwards this received data to the data processor 318 via the MAC control unit 314. For this data transmission and reception, the wireless channel interface unit 312 includes a transmitter for transmission and a receiver for reception.
In the example of FIG. 4, the data processor 302 resident at the access point 202 (see FIG. 3) likewise performs multiple different applications. In particular, the data processor 302 interfaces with external servers such as a broadcasting server and a mail server to transmit the broadcasting data 401 from the broadcasting server to the wireless terminal 204 and to forward mail data 402 from the wireless terminal 204 to the mail server. The data processor 302 also performs protocols 403 and 404 for execution and transmission of the corresponding applications 401 and 402, where protocol 403 is a resource reservation protocol and protocol 404 is a TCP/IP protocol.
The MAC control unit 306 of the access point 202, via the wireless channel interface unit 308, checks the state of the wireless channel 206 for communications and occupies the channel 206. Once the channel 206 is occupied, the wireless channel interface unit 308 transmits the broadcasting data 401 from the data processor 302 to the wireless terminal 204 over the wireless channel 206, or receives data 402 from the wireless terminal 204 and forwards the received data 402 to the data processor 302 via the MAC control unit 306. The wireless channel interface unit 308 of the access point 202 also includes a transmitter and a receiver for data transmission and reception.
When only a single wireless channel 206 is provided, a conventional wireless communication system cannot transmit data from the access point 202 to the wireless terminal 204 while simultaneously transmitting data from the wireless terminal 204 to the access point 202.
FIG. 5 depicts a frame of data that may be transmitted and received through the wireless channel 206 as part of the data flow illustrated in FIG. 4. As shown in FIG. 5, data that is transmitted and received for each of the applications is intermixed over one channel for transmission and reception.